Renewable spark plug



Nov. 27, 1934. L J, TETLow RENEWABLE SPARK PLUG Filed Oct. lO, 1930 w Y .Y A

.. III .|.IIIIl Patented Nov. 27, 1934 UNITED STATES PATENT OFFICE 4 Claims.

l tion, the replacement of which will leave the spark plug in substantially as good condition as when,

the entire device was new.

A further object of the present invention is the provision of a high grade spark plug, such, for example, as is used in airplanes, in which the insulator body is made of two telescoping sections, this provision not only giving increased insulating power but more important still permitting the use of the highest possible grade of material for the central section of the body without increasing unwarrantedly the total cost of the insulator because the outer section of the body may be made of appreciably less. expensive material while yet maintaining the highest elciency.

A still further object of the present invention consists in the provision of a core which xedly carries the electrode and which seats in a plurality of shoulders in the body, while at the same time having no permanent connection with the body and in which the electrode does not have permanent contact with the cap or terminal, in this way securing maximum ease of replacement of the electrode carrying core.

In the drawing:

Figure 1 is a central section.

Figure 2 is a bottom plan view.

Figure 3 is a central sectional view of the preferred form.

Figure 4 is a detail view of Figure 3 showing a replaceable electrode.

In spite of a number of suggested methods for replacement of the central electrode of a spark plug none of these devices have ever gone into commercial practice and it is universal with airplane practice to discard either the entire plug or, what is practically the same thing, to discard all except the shell, the latter having a value many times less than the portion which is discarded. In the present invention provision is made for discarding a portion having a total value very appreciably less than the parts which are kept in use. Experiments have shown it to be substantially impossible to discard the central electrode alone in spite of the fact that under normal conditions this is the only piece which is really worn out. Even in the present device where the core which carries this central electrode is an expensive piece, the difficulty inherent in the removal of the electrode from the core is so great that the intention is to discard the core with the electrode because it is most essential that an exact spacing be had between the central electrode and the ground electrode or electrodes and where provision is made for the knocking out of the central electrode a serious sacrifice of correct spacing must be had.

In the drawing the shell 10 is of usual design but I much prefer to use three ground electrodes 11 which are merely pins radially positioned near the cylinder end of the plug and as is not unusual these pins are adjustable in and out in a radial direction in order to secure extremely ne adjustment. The couple:` nut l2 differs from usual practice in that it permanently carries the top insulator section 14 which has a threaded engagement 15 with the coupler nut and in addition is permanently secured to the metal bushing or nut by cementing and packing so that to all intents and purposes the coupler nut and the top insulator section are integral and carry permanently with them the mica washers 16, the primary purpose of which is to act as heat insulators. The copper gasket 17 is of usual form making a gas tight joint between the coupler nut 12 and the seat 18 in the shell.

The top insulator section 14, which is the body, is hollow preferably having two central bores, the

larger major bore receiving snugly the sleeve section 20 of the core while the smaller and upper bore receives snugly the mercury cup 22 which is fitted to the cap 23 by a forced tting 0f its small central holding lug 24. Altho inverted this cup 22 will not discharge its mercury. The cap 23 has a threaded engagement with the cylindrical head 26 of the body 14 but the cap makes contact with the central electrode 27 only thru the mercury in the cup 22. A terminal 28 is fitted to the screw portion 29 of the cap 23 and may receive a wire beneath it but in airplane practice it is customary to use a rajah clip, the insulating sleeve of which is numbered 30, the fork 31 and the holding spring 32. While I make no change whatsoever in the rajah snapon fastener I do strongly prefer to add the nut 33, the function of which is not to hold the fastener to the terminal by any binding force but merely to prevent the spring steel holding member 32 from rising. The nut 33 may either be plain or having a slight counterbore, the latter being the preferred form, as it presses the spring 32 rmly against the fork 31.

The lower portion of the bottom insulator or core 20 is conical forming a decided shoulder 35 between the conical portion 36 and the upper cylindrical portion 20. This shoulder 35 is in rm engagement with a metal plate 38 which fits snugly in a counterbore in the lower portion of the metal coupler nut 12 but is of such diameter as not to engage the copper gasket 17. The bottom insulator or core 20 preferably is made of the nest grade of porcelain alt-ho obviously it can be made of other insulating material, The body 14 may be, and preferably is, made of insulating material of a lower grade for it is relieved of stress and is not subject vto the same degree of heat as is the bottom insulator or core. While I prefer to t the bottom insulator or core 20 to the top insulator or body 14 merely by friction I may apply a small amount or" cement between the two sections of the insulator to 'no-ld them in place during normal use while permitting the core to be readily knocked out of the body for replacement.

The central electrode 27 is permanently secured to the sleeve portion 2i) of the core but is loose in the integral lower conical section 36 of the core to allow for expansion or" the metal. The looseness naturally is the least possible but there must be some freedom because the coefficients of the central electrode and the porcelain cannot be made absolutely-the same altho they can be closely approximated. On the central electrode near its top are two collars 4c and 41, the latter engaging snugly the sleeve portion 2G of the core and the former holding a mica washer 42 inplace against the mercury cup 22. Either or both of these collars may be omitted but I prefer to use both of them. IIhey are preierably of brass or copper and held to the electrode by shrinking. The tightness of fit however is not so great but that I can move either of the collars longitudinally of the electrode when necessary to secure the desired spacing.

Ordinarily a spark plug in airplane use becomes unsatisfactory because of two reasons, one that the central electrode is pitted or worn and the other that the mica bottom tip of the electrode becomes cil soaked. Under such conditions the entire plug is thrown away. With my plug the shell, body and cap are saved land only the core 20 with its permanentiy secured electrode is thrown away. As previously stated the core itself is not in any way damaged but I find thru repeated trials it is not worth while to drive the one central electrode from the core and replace it since the labor cost is greater than the value of the porcelain core. The electrode can, however, be removed and a new electrode driven thru the core and cemented toit. I strongly prefer, however, to replace the core and electrode as a unit because the electrode is packed in the core and by replacing both I secure an absolutely tight iitting, there being an asbestos wick between the core and the shoulder at the top of the body. The metal plate 33 is permanently secured tov the body 14 and itsprirnary function is to prevent the transfer or pressure from the conical portion 36 of the bottoni insulator direct to the body 14 but to transmit this pressure to the metal coupler nut 12 which in turn transfers the pressure to the metal shell l0. It will be noted there is no connection whatsoever between the central metal electrode 27 and the metal of the cap save thru the liquid metal which is contained in the cup 22.

In the modified form of Figure 3 the shell is omitted, 47 is the tcp section of the insulator and 48 is the lower section, these members corresponding to the body 14 and core 20. A long screw 50 having a kerfed head 51 extends entirely thru the device shown and up to the terminal 53 is surrounded by a hollow sleeve 54 of mica. Between the head 51 and the bottom of the inside insulating member 48 is an insulation 55 made up of mica disks, this cllowing the usual practice of having disk mica near the central electrode 56 which, in this case, is drive fitted to the head 5l of the bolt. The metal coupler nut 57 receives the larger cylindrical portion 58 of the innerv insulating member 48 and preferably carries a packing of mica 59 between it and the hollow conical outer insulating sleeve 47. The device is held together by screwing down the brass terminal 53 which secures together the various parts. This terminal 53' is not used to secure a wire below it but is provided with the usual groove 60 to receive a snap-on fastener as in the preferred model. To replace the worn portion of this spark plug the brass terminal nut 53 is removed from the screw 50 and the screw is then removed carrying with it the oil soaked mica 55 and the porcelain core 48. The body 47 and nut 57 are used again as is the shell and the terminal.

A very similar structure is shown in Figure 4, the only difference being that in this case the screw 50 is made in two parts, 50h which is a rod threaded only at its top to receive the terminal 53 and tapped at its bottom to receive the threaded portion 50a of the screw, the head 51 being the same and carrying the central electrode 56. In'

.this modied form a metal washer 62 is threaded to the screw 50a and binds in place the disk mica 55 and. the sleeve mica 54. In this form the core 48 is not discarded but when replacement is necessary only the screw 50a, the nut 62, the mica 55 10U and the electrode 56 are replaced.

What I claim is:

l. In a separable spark plug insulator, a body of insulating material having a bore therein, a core section of insulating material separably telescoping within the body, substantially its entire length, la central electrode permanently fixed within the core, a bushing surrounding the lower end of said core section, a head on the lower end of the electrode engaging the lower end of the 1.10 core, and a terminal nut threaded on the upper end of the electrode, said terminal nut having a broad base for engaging the upper end of the core and the insulator body whereby said electrode serves tobind the parts together. M5

2. A replaceable electrode carrying insulator section consisting of a headed screw, a sleeve of mica surrounding the screw, a series of mica disks surrounding the sleeve, an insulator nut threaded on the stem of the screw and binding in place the mica disks, and an electrode carried by the head of the screw, said screw having its threaded portion extending beyond said nut whereby the section may be connected to a main electrode.

3. In a spark plug, a central rod tapped on one end, said rod having threads on the other end, a tube of mica ttingsaid rod, an insulator core tting over said tube, a coupler nut engaging said core and adapted to screw into a shell, an insulator sleeve telescoped over the upper part of said iii? core, a removable tip on said core comprising an insulator body having a central screw for engag-v ing the tapped end of said rod and serving-as a head therefor, and a nut on said rod for drawing together'the core, sleeve, coupler nut and said tip.

4. In a spark plug, a coupler nut, an insulator body above the coupler nut, a second insulator body telescoped within the iirst mentioned body and within the coupler nut, a third insulator body below the coupler nut, a headed member extend.- ing thru the insulator bodies and the coupler nut, means above the top insulator body and threadedto the headed member for binding together the insulating bodies, a mica sleeve around the member and extending from the head to said binding means, and an electrode section carried by the headed member, said headed member being in two detachable sections, one or" which is removable with the third insulator body and the electrode, LEWIS J. TE'ILOW. 359 

